The present invention relates to mechanized farming machines commonly called brush cutters and edge trimmers, intended for cutting vegetation by means of cutting lines. This invention relates more particularly to the rotary cutting heads for such machines.
These machines are generally equipped with an internal combustion engine or electric motor which rotates, at a high speed possibly of between approximately 3000 revolutions per minute and 12,000 revolutions per minute, a rotary head supporting one or more cutting lines. During rotation of the head, and owing to the effect of the centrifugal force, the cutting line or lines are deployed radially and thus sweep a certain circular region within which they exert a cutting effect on the vegetation encountered.
At the present time, two broad categories of cutting heads are known for this kind of machine. The first type of head contains a reel of cutting line, which can be gradually paid out as the line used becomes worn or breaks. The second known type of head, to which the present invention also applies, does not use a reel of line but only one or more relatively short cutting line filaments which have to be fixed individually to the head. With regard to the latter type of cutting head, reference may be made to documents U.S. Pat. No. 4,513,563, NL-A-8,302,111, GB-A-2,214,048 and GB-A-1,583,521. In some of these documents, the cutting line filaments are folded in their middle, which also constitutes their fastening region, so that each forms two parallel cutting line portions approximately of the same length.
Reference may also be made here to document DE-A-2,444,610 (FIG. 2), which relates to a mower and not to a brush cutter or an edge trimmer, and in which the two parallel portions of the wire filament, which forms a loop, are linked together so that these portions do not form two separate flexible cutting elements but form a single, rigid, cutting member. This embodiment remains, structurally and operationally, remote from the subject-matter of the present invention, as defined below.
All the current cutting heads, with or without a reel of cutting line, are difficult to reload, and/or are of complicated and expensive structure, and also pose various problems.
Among others, conventional cutting lines, in the form of smooth monofilaments, are noisy in operation and thus generate noise pollution. In order to try to reduce the operating noise, the current lines of research consist in providing cutting lines with a special, generally non-smooth, shape: corrugated lines, ribbed or grooved lines, lines with a granular coating, etc.
Considering more particularly the constructions in the aforementioned documents U.S. Pat. No. 4,513,563, NL-A-8,302,111, GB-A-2,214,048 and GB-A-1,583,521, it is found that the two parallel portions of each folded line filament always lie in two separate planes, perpendicular to the axis of the head, that is to say they have a certain axial offset one with respect to the other and are not contained in the same plane perpendicular to the axis of the head. Such a configuration does not allow the operating noise of the cutting head to be reduced.
Now, it has been found, surprisingly, that the arrangement of two free line portions placed xe2x80x9cin parallelxe2x80x9d, and in the same plane, resulted in an appreciable reduction in the noise level during operation, even when using a smooth line of ordinary cross section (round or square).
Starting from this observation, the subject of the invention is a cutting head for brush cutters or edge trimmers, of the kind using relatively short cutting line filaments, individually retained on the head, wherein the cutting line filament or filaments form one or more pairs of parallel cutting line portions approximately of the same length, which are free and extend in the same plane perpendicular to the axis of the head, so as to reduce the sound level during operation.
Thus, the proximity (which varies depending on the diameter) of the cutting line portions, combined in pairs, creates an interaction between the turbulence from each line portion, which reduces the tendency of these line portions to vibrate: the turbulence from the line portion lying upstream (with respect to the direction of rotation of the head) xe2x80x9cblocksxe2x80x9dthe turbulence from the line portion lying downstream, and consequently reduces the overall turbulence and the noise generated. Tests carried out by the Applicant have confirmed the reality of this phenomenon, and its permanence over time, during rotation of the head.